Process for producing polyolefins

ABSTRACT

A novel process for producing homopolymers and interpolymers of olefins which involves contacting an olefin and/or an olefin and at least one or more other olefin(s) under polymerization conditions with a metallocene catalyst and dinitrogen monoxide in amounts sufficient to reduce the electrostatic charge in the polymerization medium. Also provided is a process for reducing electrostatic charge in the production of polyolefins by introducing dinitrogen monoxide into the polymerization medium.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part application of application Ser. No.09/387,598 filed on Aug. 31, 1999 now abandoned, the entire content ofwhich is hereby incorporated by reference. Related are U.S. Pat. Nos.6,187,879 and 6,191,238.

FIELD OF INVENTION

The present invention relates to a polymerization process for theproduction of polyolefins utilizing a metallocene catalyst anddinitrogen monoxide (N₂O) in amounts sufficient to reduce theelectrostatic charge in the polymerization reactor. The use ofdinitrogen monoxide as a catalytic agent further provides polyolefinsthat are suitable for molding and film applications.

BACKGROUND OF INVENTION

Polyolefins such as polyethylene are well known and are useful in manyapplications. In particular, linear polyethylene polymers possessproperties which distinguish them from other polyethylene polymers, suchas branched ethylene homopolymers commonly referred to as LDPE (lowdensity polyethylene). Certain of these properties are described byAnderson et al, U.S. Pat. No. 4,076,698.

A particularly useful polymerization medium for producing polyethyleneand polypropylene polymers is a gas phase process. Examples of such aregiven in U.S. Pat. Nos. 3,709,853; 4,003,712; 4,011,382; 4,302,566;4,543,399; 4,882,400; 5,352,749 and 5,541,270 and Canadian Patent No.991,798 and Belgian Patent No. 839,380.

Metallocene catalysts are known for polymerizing and interpolymerizingolefins such as ethylene. Metallocene catalysts comprise at least onetransition metal component having at least one moiety selected fromsubstituted or unsubstituted cyclopentadienyl, substituted orunsubstituted pentadienyl, substituted or unsubstituted pyrrole,substituted or unsubstituted phosphole, substituted or unsubstitutedarsole, substituted or unsubstituted boratabenzene, and substituted orunsubstituted carborane, and at least one co-catalyst component. Typicalorganometallic co-catalysts are alkyl aluminoxanes, such as methylaluminoxane, and boron containing compounds such astris(perfluorophenyl)boron and salts of tetrakis(perfluorophenyl)borate.

The metallocene catalysts can be supported on an inert porousparticulate carrier

A generally encountered problem in polymerization processes, inparticular gas phase polymerization processes, is the formation ofagglomerates. Agglomerates can form in various places such as thepolymerization reactor and the lines for recycling the gaseous stream.As a consequence of agglomerate formation it may be necessary to shutdown the reactor.

When agglomerates form within the polymerization reactor there can bemany adverse effects. For example, the agglomerates can disrupt theremoval of polymer from the polymerization reactor by plugging thepolymer discharge system. Further, if the agglomerates fall and coverpart of the fluidization grid a loss of fluidization efficiency mayoccur. This can result in the formation of larger agglomerates which canlead to the loss of the entire fluidized bed. In either case there maybe the necessity for the shutdown of the reactor.

It has been found that agglomerates may be formed as a result of thepresence of very fine polymer particles in the polymerization medium.These fine polymer particles may be present as a result of introducingfine catalyst particles or breakage of the catalyst within thepolymerization medium.

These fine particles are believed to deposit onto and electrostaticallyadhere to the inner walls of the polymerization reactor and theassociated equipment for recycling the gaseous stream such as, forexample, the heat exchanger. If the fine particles remain active, andthe polymerization reaction continues, then the particles will grow insize resulting in the formation of agglomerates. These agglomerates whenformed within the polymerization reactor tend to be in the form ofsheets.

Several solutions have been proposed to resolve the problem of formationof agglomerates in gas phase polymerization processes. These solutionsinclude the deactivation of the fine polymer particles, control of thecatalyst activity and the reduction of the electrostatic charge.Exemplary of the solutions are as follows.

European Patent Application 0 359 444 A1 describes the introduction intothe polymerization reactor of small amounts of an activity retarder inorder to keep substantially constant either the polymerization rate orthe content of transition metal in the polymer produced. The process issaid to produce a polymer without forming agglomerates.

U.S. Pat. No. 4,739,015 describes the use of gaseous oxygen containingcompounds or liquid or solid active-hydrogen containing compounds toprevent the adhesion of the polymer to itself or to the inner wall ofthe polymerization apparatus.

In U.S. Pat. No. 4,803,251 there is described a process for reducingsheeting utilizing a group of chemical additives which generate bothpositive and negative charges in the reactor, and which are fed to thereactor in an amount of a few parts per million (ppm) per part of themonomer in order to prevent the formation of undesired positive ornegative charges.

Other processes and other additives that may be used to neutralizeelectrostatic charge in the fluidized-bed reactor are found in U.S. Pat.Nos. 4,792,592; 4,803,251; 4,855,370; 4,876,320; 5,162,463; 5,194,526and 5,200,477.

Additional processes for reducing or eliminating electrostatic chargeinclude (1) installation of grounding devices in a fluidized bed, (2)ionization of gas or particles by electrical discharge to generate ionswhich neutralize electrostatic charge on the particles and (3) the useof radioactive sources to produce radiation capable of generating ionswhich neutralize electrostatic charge on the particles.

It would be desirable therefore to provide a process for producingpolyolefins, particularly polyethylene, wherein the problems associatedwith electrostatic charge are reduced.

SUMMARY OF THE INVENTION

The polymerization process of the present invention comprises theintroduction into a polymerization medium comprising an olefin,particularly ethylene, and optionally at least one or more otherolefin(s), at least one metallocene catalyst comprising at least onetransition metal component having at least one moiety selected fromsubstituted or unsubstituted cyclopentadienyl, substituted orunsubstituted pentadienyl, substituted or unsubstituted pyrrole,substituted or unsubstituted phosphole, substituted or unsubstitutedarsole, substituted or unsubstituted boratabenzene, and substituted orunsubstituted carborane, and at least one co-catalyst component, anddinitrogen monoxide (N₂O), wherein the dinitrogen monoxide is present inan amount sufficient to reduce the electrostatic charge in thepolymerization medium to a level lower than would occur in the samepolymerization process in the absence of the dinitrogen monoxide.

The present invention also relates to a process for reducingelectrostatic charge in a polymerization medium comprising an olefin,particularly ethylene, and optionally at least one or more otherolefin(s), at least one metallocene catalyst comprising at least onetransition metal component having at least one moiety selected fromsubstituted or unsubstituted cyclopentadienyl, substituted orunsubstituted pentadienyl, substituted or unsubstituted pyrrole,substituted or unsubstituted phosphole, substituted or unsubstitutedarsole, substituted or unsubstituted boratabenzene, and substituted orunsubstituted carborane, and at least one co-catalyst component, anddinitrogen monoxide (N₂O), comprising introducing the dinitrogenmonoxide into the polymerization medium in an amount sufficient toreduce electrostatic charge in the polymerization medium to a levellower than would occur in the same polymerization process in the absenceof the dinitrogen monoxide.

All mention herein to elements of Groups of the Periodic Table are madein reference to the Periodic Table of the Elements, as published in“Chemical and Engineering News”, 63(5), 27, 1985. In this format, theGroups are numbered 1 to 18.

DETAILED DESCRIPTION OF THE INVENTION

The polymerization process of the present invention comprises theintroduction into a polymerization medium comprising an olefin,particularly ethylene, and optionally at least one or more otherolefin(s), at least one metallocene catalyst comprising at least onetransition metal component having at least one moiety selected fromsubstituted or unsubstituted cyclopentadienyl, substituted orunsubstituted pentadienyl, substituted or unsubstituted pyrrole,substituted or unsubstituted phosphole, substituted or unsubstitutedarsole, substituted or unsubstituted boratabenzene, and substituted orunsubstituted carborane, and at least one co-catalyst component, anddinitrogen monoxide (N₂O), wherein the dinitrogen monoxide is present inan amount sufficient to reduce the electrostatic charge in thepolymerization medium to a level lower than would occur in the samepolymerization process in the absence of the dinitrogen monoxide.

The present invention also relates to a process for reducingelectrostatic charge in a polymerization medium comprising an olefin,particularly ethylene, and optionally at least one or more otherolefin(s), at least one metallocene catalyst comprising at least onetransition metal component having at least one moiety selected fromsubstituted or unsubstituted cyclopentadienyl, substituted orunsubstituted pentadienyl, substituted or unsubstituted pyrrole,substituted or unsubstituted phosphole, substituted or unsubstitutedarsole, substituted or unsubstituted boratabenzene, and substituted orunsubstituted carborane, and at least one co-catalyst component, anddinitrogen monoxide (N₂O), comprising introducing the dinitrogenmonoxide into the polymerization medium in an amount sufficient toreduce electrostatic charge in the polymerization medium to a levellower than would occur in the same polymerization process in the absenceof the dinitrogen monoxide.

The polymerization reaction of the present invention is carried out inthe presence of at least one metallocene catalyst. In the process of theinvention, the catalyst can be introduced in any manner known in theart. For example, the catalyst can be introduced directly into thefluidized bed reactor in the form of a solution, a slurry or a dry freeflowing powder. The catalyst can also be used in the form of adeactivated catalyst, or in the form of a prepolymer obtained bycontacting the catalyst with one or more olefins in the presence of aco-catalyst.

Metallocene catalysts are well known in the industry and are comprisedof at least one transition metal component and at least one co-catalystcomponent. The transition metal component of the metallocene catalystcomprises a compound having at least one moiety selected fromsubstituted or unsubstituted cyclopentadienyl, substituted orunsubstituted pentadienyl, substituted or unsubstituted pyrrole,substituted or unsubstituted phosphole, substituted or unsubstitutedarsole, substituted or unsubstituted boratabenzene, and substituted orunsubstituted carborane, and at least one transition metal. Preferablythe moiety is a substituted or unsubstituted cyclopentadienyl. Thetransition metal is selected from Groups 3, 4, 5, 6, 7, 8, 9 and 10 ofthe Periodic Table of the Elements. Exemplary of such transition metalsare scandium, titanium, zirconium, hafnium, vanadium, chromium,manganese, iron, cobalt, nickel, and the like, and mixtures thereof. Ina preferred embodiment the transition metal is selected from Groups 4, 5or 6 such as, for example, titanium, zirconium, hafnium, vanadium andchromium, and in a still further preferred embodiment, the transitionmetal is titanium or zirconium or mixtures thereof.

The co-catalyst component of the metallocene catalyst can be anycompound, or mixtures thereof, that can activate the transition metalcomponent(s) of the metallocene catalyst in olefin polymerization.Typically the co-catalyst is an alkylaluminoxane such as, for example,methylaluminoxane (MAO) and aryl substituted boron containing compoundssuch as, for example, tris(perfluorophenyl)borane and the salts oftetrakis(perfluorophenyl)borate.

There are many references describing metallocene catalysts in greatdetail. For example, metallocene catalysts are described in U.S. Pat.Nos. 4,564,647; 4,752,597; 5,106,804; 5,132,380; 5,227,440; 5,296,565;5,324,800; 5,331,071; 5,332,706; 5,350,723; 5,399,635; 5,466,766;5,468,702; 5,474,962; 5,578,537 and 5,863,853. The entire contents ofthese patents are incorporated herein by reference.

The metallocene catalysts herein also include catalyst systems such as[C₅H₅B—OEt]₂ZrCl₂, [C₅H₄CH₂CH₂NMe₂]TiCl₃, [PC₄Me₃Si(Me)₂NCMe₃]ZrCl₂,[C₅Me₄Si(Me)₂NCMe₃]TiCl₂, and (C₅H₅)(C₅H₇)ZrCl₂.

The metallocene catalysts herein can be introduced in the process of thepresent invention in any manner. For example, the catalyst componentscan be introduced directly into the polymerization medium in the form ofa solution, a slurry or a dry free flowing powder. The transition metalcomponent(s) and the co-catalyst component(s) of the metallocenecatalyst can be premixed to form an activated catalyst prior to additionto the polymerization medium, or the components can be added separatelyto the polymerization medium, or the components can be premixed and thencontacted with one or more olefins to form a prepolymer and then addedto the polymerization medium in prepolymer form. When the catalystcomponents are premixed prior to introduction into the reactor, anyelectron donor compound may be added to the catalyst to control thelevel of activity of the catalyst. Furthermore, there may be addedadditional organometallic compounds, such as trialkylaluminums, to thepolymerization medium.

Any or all of the components of the metallocene catalyst can besupported on a carrier. The carrier can be any particulate organic orinorganic material. Preferably the carrier particle size should not belarger than about 200 microns in diameter. The most preferred particlesize of the carrier material can be easily established by experiment.Preferably, the carrier should have an average particle size of 5 to 200microns in diameter, more preferably 10 to 150 microns and mostpreferably 20 to 100 microns.

Examples of suitable inorganic carriers include metal oxides, metalhydroxides, metal halogenides or other metal salts, such as sulphates,carbonates, phosphates, nitrates and silicates. Exemplary of inorganiccarriers suitable for use herein are compounds of metals from Groups 1and 2 of the Periodic Table of the Elements, such as salts of sodium orpotassium and oxides or salts of magnesium or calcium, for instance thechlorides, sulphates, carbonates, phosphates or silicates of sodium,potassium, magnesium or calcium and the oxides or hydroxides of, forinstance, magnesium or calcium. Also suitable for use are inorganicoxides such as silica, titania, alumina, zirconia, chromia, boron oxide,silanized silica, silica hydrogels, silica xerogels, silica aerogels,and mixed oxides such as talcs, silica/chromia, silica/chromia/titania,silica/alumina, silica/titania, silica/magnesia,silica/magnesia/titania, aluminum phosphate gels, silica co-gels and thelike. The inorganic oxides may contain small amounts of carbonates,nitrates, sulfates and oxides such as Na₂CO₃, K₂CO₃, CaCO₃, MgCO₃,Na₂SO₄, Al₂(SO₄)₃, BaSO₄, KNO₃, Mg(NO₃)₂, Al(NO₃)₃, Na₂O, K₂O and Li₂O.Carriers comprising at least one component selected from the groupconsisting of SiO₂, Al₂O₃ or mixtures thereof as a main component arepreferred.

Examples of suitable organic carriers include polymers such as, forexample, polyethylene, polypropylene, copolymers of ethylene andalpha-olefins, polystyrene, and functionalized polystyrene.

The metallocene catalyst may be prepared by any method known in the art.The catalyst can be in the form of a solution, a slurry or a dry freeflowing powder. The amount of metallocene catalyst used is that which issufficient to allow production of the desired amount of the polyolefin.

Any halogenated hydrocarbon may be used in the process of the presentinvention. If desired more than one halogenated hydrocarbon can be used.Typical of such halogenated hydrocarbons are monohalogen and polyhalogensubstituted saturated or unsaturated aliphatic, alicyclic, or aromatichydrocarbons having 1 to 12 carbon atoms. Preferred for use in theprocess of the present invention are dichloromethane, chloroform, carbontetrachloride, chlorofluoromethane, chlorodifluromethane,dichlorodifluoromethane, fluorodichloromethane, chlorotrifluoromethane,fluorotrichloromethane and 1,2-dichloroethane. Most preferred for use inthe process of the present invention is chloroform.

In carrying out the polymerization process of the present invention theco-catalyst(s) is added to the transition metal component of themetallocene catalyst in any amount sufficient to effect production ofthe desired polyolefin. It is preferred to utilize the co-catalyst(s) ina molar ratio of co-catalyst(s) to the transition metal componentranging from about 0.5:1 to about 10000:1. In a more preferredembodiment, the molar ratio of co-catalyst(s) to transition metalcomponent ranges from about 0.5:1 to about 1000:1.

The polymerization process of the present invention may be carried outusing any suitable process, for example, solution, slurry and gas phase.A particularly desirable method for producing polyolefin polymersaccording to the present invention is a gas phase polymerization processpreferably utilizing a fluidized bed reactor. This type reactor andmeans for operating the reactor are well known and completely describedin U.S. Pat. Nos. 3,709,853; 4,003,712, 4,011,382; 4,012,573; 4,302,566;4,543,399; 4,882,400; 5,352,749; 5,541,270; Canadian Patent No. 991,798and Belgian Patent No. 839,380. These patents disclose gas phasepolymerization processes wherein the polymerization medium is eithermechanically agitated or fluidized by the continuous flow of the gaseousmonomer and diluent. The entire contents of these patents areincorporated herein by reference.

In general, the polymerization process of the present invention may beeffected as a continuous gas phase process such as a fluid bed process.A fluid bed reactor for use in the process of the present inventiontypically comprises a reaction zone and a so-called velocity reductionzone. The reaction zone comprises a bed of growing polymer particles,formed polymer particles and a minor amount of catalyst particlesfluidized by the continuous flow of the gaseous monomer and diluent toremove heat of polymerization through the reaction zone. Optionally,some of the recirculated gases may be cooled and compressed to formliquids that increase the heat removal capacity of the circulating gasstream when readmitted to the reaction zone. A suitable rate of gas flowmay be readily determined by simple experiment. Make up of gaseousmonomer to the circulating gas stream is at a rate equal to the rate atwhich particulate polymer product and monomer associated therewith iswithdrawn from the reactor and the composition of the gas passingthrough the reactor is adjusted to maintain an essentially steady stategaseous composition within the reaction zone. The gas leaving thereaction zone is passed to the velocity reduction zone where entrainedparticles are removed. Finer entrained particles and dust may be removedin a cyclone and/or fine filter. The gas is passed through a heatexchanger wherein the heat of polymerization is removed, compressed in acompressor and then returned to the reaction zone.

In more detail, the reactor temperature of the fluid bed process hereinranges from about 30° C. to about 150° C. In general, the reactortemperature is operated at the highest temperature that is feasibletaking into account the sintering temperature of the polymer productwithin the reactor.

The process of the present invention is suitable for the production ofhomopolymers of olefins, particularly ethylene, and/or copolymers,terpolymers, and the like, of olefins, particularly ethylene, and atleast one or more other olefin(s). Preferably the olefins arealpha-olefins. The olefins, for example, may contain from 2 to 16 carbonatoms. Particularly preferred for preparation herein by the process ofthe present invention are polyethylenes. Such polyethylenes arepreferably homopolymers of ethylene and interpolymers of ethylene and atleast one alpha-olefin wherein the ethylene content is at least about50% by weight of the total monomers involved. Exemplary olefins that maybe utilized herein are ethylene, propylene, 1-butene, 1-pentene,1-hexene, 1-heptene, 1-octene, 4-methylpent-1-ene, 1-decene, 1-dodecene,1-hexadecene and the like. Also utilizable herein are polyenes such as1,3-hexadiene, 1,4-hexadiene, cyclopentadiene, dicyclopentadiene,4-vinylcyclohex-1-ene, 1,5-cyclooctadiene, 5-vinylidene-2-norbornene and5-vinyl-2-norbornene, and olefins formed in situ in the polymerizationmedium. When olefins are formed in situ in the polymerization medium,the formation of polyolefins containing long chain branching may occur.

In carrying out the polymerization process of the present invention thedinitrogen monoxide utilized to reduce electrostatic charge in thepolymerization medium is added in any manner. For example, thedinitrogen monoxide may be added to the preformed catalyst, to theprepolymer during the prepolymerization step, to the preformedprepolymer and/or to the polymerization medium. The dinitrogen monoxidemay optionally be premixed with the co-catalyst when utilized. Thedinitrogen monoxide is added in any amount sufficient to reduce theelectrostatic charge in the polymerization medium to a level lower thanwould occur in the same polymerization process in the absence of thedinitrogen monoxide. It is preferred to incorporate the dinitrogenmonoxide in the polymerization medium in an amount ranging from about 1ppm to about 10,000 ppm by volume.

In carrying out the polymerization process of the present invention, thehalogenated hydrocarbon may be added to the polymerization medium in anyamount sufficient to effect production of the desired polyolefin. It ispreferred to incorporate the halogenated hydrocarbon in a molar ratio ofhalogenated hydrocarbon to transition metal component of the metallocenecatalyst ranging from about 0.001:1 to about 10:1. In a more preferredembodiment, the molar ratio of halogenated hydrocarbon to transitionmetal component ranges from about 0.001:1 to about 10:1.

The molecular weight of the polyolefin produced by the present inventioncan be controlled in any known manner, for example, by using hydrogen.The molecular weight control of polyethylene, for example, may beevidenced by an increase in the melt index (I₂) of the polymer when themolar ratio of hydrogen to ethylene in the polymerization medium isincreased.

Any conventional additive may be added to the polyolefins obtained bythe present invention. Examples of the additives include nucleatingagents, heat stabilizers, antioxidants of phenol type, sulfur type andphosphorus type, lubricants, antistatic agents, dispersants, copper harminhibitors, neutralizing agents, foaming agents, plasticizers,anti-foaming agents, flame retardants, crosslinking agents, flowabilityimprovers such as peroxides, ultraviolet light absorbers, lightstabilizers, weathering stabilizers, weld strength improvers, slipagents, anti-blocking agents, antifogging agents, dyes, pigments,natural oils, synthetic oils, waxes, fillers and rubber ingredients.

The polyolefins, particularly polyethylenes, of the present inventionmay be fabricated into films by any technique known in the art. Forexample, films may be produced by the well known cast film, blown filmand extrusion coating techniques.

Further, the polyolefins, particularly polyethylenes, may be fabricatedinto other articles of manufacture, such as molded articles, by any ofthe well known techniques.

The invention will be more readily understood by reference to thefollowing examples. There are, of course, many other forms of thisinvention which will become obvious to one skilled in the art, once theinvention has been fully disclosed, and it will accordingly berecognized that these examples are given for the purpose of illustrationonly, and are not to be construed as limiting the scope of thisinvention in any way.

EXAMPLES Polymerization Process

The polymerization process utilized in Examples 1-28 herein is carriedout in a fluidized-bed reactor for gas-phase polymerization, consistingof a vertical cylinder of diameter 0.74 meters and height 7 meters andsurmounted by a velocity reduction chamber. The reactor is provided inits lower part with a fluidization grid and with an external line forrecycling gas, which connects the top of the velocity reduction chamberto the lower part of the reactor, at a point below the fluidizationgrid. The recycling line is equipped with a compressor for circulatinggas and a heat transfer means such as a heat exchanger. In particularthe lines for supplying ethylene, an olefin such as 1-butene, 1-penteneand 1-hexene, hydrogen and nitrogen, which represent the mainconstituents of the gaseous reaction mixture passing through thefluidized bed, feed into the recycling line. The dinitrogen monoxideutilized to reduce electrostatic charge is fed directly into therecycling line. Above the fluidization grid, the reactor contains afluidized bed consisting of a polyethylene powder made up of particleswith a weight-average diameter of about 0.5 mm to about 1.4 mm. Thegaseous reaction mixture, which contains ethylene, olefin comonomer,hydrogen, nitrogen and minor amounts of other components, passes throughthe fluidized bed under a pressure ranging from about 280 psig to about300 psig with an ascending fluidization speed, referred to herein asfluidization velocity, ranging from about 1.6 feet per second to about2.0 feet per second.

The electrostatic charge of the fluidized bed was measured by aCorreflow Model 3400 Electrostatic Monitor (ESM) supplied by AuburnInternational, Inc. of Danvers, Mass. The electrostatic probe wasinstalled in the vertical cylindrical section of the reactor at a heightsuch as to be within the fluidized bed of polymer particles. Theelectrostatic probe measures the current flow between the polymerizationmedium and the ground. A reduction in electrostatic charge is defined asa reduction in the absolute magnitude of the measured current and/or areduction in the variability of the measured current.

Example 1

The polymerization process is carried out as described above. Theolefins used herein are ethylene and 1-hexene. Hydrogen is used tocontrol molecular weight. The metallocene catalyst containsbis(1-butyl-3-methylcyclopentadienyl)zirconium dichloride andmethylaluminoxane supported on silica. An ethylene/1-hexene interpolymercan be prepared under these conditions.

The level of electrostatic charge in the polymerization reactor ismeasured. Thereafter, dinitrogen monoxide is added to the polymerizationmedium and the level of electrostatic charge is expected to be reduced.

Example 2

The process of Example 1 is followed with the exception that 1-hexene isnot utilized and a homopolymer of ethylene can be produced. The level ofelectrostatic charge in the polymerization reactor is measured.Thereafter, dinitrogen monoxide is added to the polymerization mediumand the level of electrostatic charge is expected to be reduced.

Examples 3-7

The process of Example 1 is followed with the exception that in place ofthe 1-hexene there is utilized the following comonomers:

Example 3 propylene, Example 4 1-butene, Example 5 1-pentene, Example 64-methylpent-1-ene, Example 7 1-octene.

In each of the above Examples 3-7 the level of electrostatic charge inthe polymerization medium is expected to be reduced as a result ofincorporating dinitrogen monoxide in the polymerization medium.

Examples 8-28

The process of Example 1 is followed with the exception that thesupported metallocene catalyst is replaced with the following silicasupported metallocene catalysts:

Example 8 bis(1-butyl-3- methylcyclopentadienyl)dimethylzirconium andtris(perfluorophenyl)borane, Example 9 bis(1-butyl-3-methylcyclopentadienyl)dimethylzirconium and triphenylmethyliumtetrakis(perfluorophenyl)borate, Example 10(tert-butylamido)dimethyl(tetramethyl-η⁵-cyclopentadienyl)silanetitaniumdimethyl and triphenylmethyliumtetrakis(perfluorophenyl)borate, Example 11(tert-butylamido)dimethyl(tetramethyl-η⁵-cyclopentadienyl)silanetitaniumdimethyl and tris(perfluorophenyl)borane,Example 12 (tert-butylamido)dimethyl(tetramethyl-η⁵-cyclopentadienyl)silanetitaniumdimethyl and methylaluminoxane. Example13 bis(indenyl)zirconium dichloride and methylaluminoxane. Example 14bis(fluorenyl)zirconium dichloride and methylaluminoxane. Example 15cyclopentadienyl(1-methylboratabenzene)zirconium dichloride andmethylaluminoxane. Example 16 cyclopentadienyl(1-methyl-2-trimethylsilylboratabenzene)zirconium dichloride and methylaluminoxane.Example 17 cyclopentadienyl(3,4- dimethylphospholyl)zirconium dichlorideand methylaluminoxane. Example 18 cyclopentadienyl(2,3,4,5-tetramethylphospholyl)zirconium dichloride and methylaluminoxane.Example 19 bis(2,3,4,5-tetramethylphospholyl)zirconium dichloride andmethylaluminoxane. Example 20 bis(2,5-diphenyl-3-methylphospholyl)zirconium dichloride and methylaluminoxane. Example 21pentamethylcyclopentadienyl(2,3,4,5- tetramethylarsolyl)zirconiumdichloride and methylaluminoxane. Example 22bis(2,3,4,5-tetramethylarsolyl)zirconium dichloride andmethylaluminoxane. Example 23 bis(2,3,-dimethylarsolyl)zirconiumdichloride and methylaluminoxane. Example 24bis(2,3,4,5-tetramethylpyrrolyl)zirconium dichloride andmethylaluminoxane. Example 25 pentamethylcyclopentadienyl(2,3,4,5-tetramethylpyrrolyl)zirconium dichloride and methylaluminoxane. Example26 pentamethylcyclopentadienyl[(7,8,9,10,11-η)-undecahydro-7,8-dicarbaundecaborato(2- )]methylzirconium Example 27(N-tert-butylamido)(dimethyl)(2,4-dimethyl-η₅-pentadien-1-yl)silanetitanium(IV) dichloride and methylaluminoxane.Example 28 (N-tert-butylamido)(dimethyl)(2,4-dimethyl-η₅-pentadien-3-yl)silanetitanium(IV) dimethyl and methylaluminoxane.

In each of the above Examples 8-28 the level of electrostatic charge inthe polymerization medium is expected to be reduced as a result ofincorporating dinitrogen monoxide in the polymerization medium.

Films can be prepared from the polyolefins of the present invention.

Articles such as molded items can also be prepared from the polyolefinsof the present invention.

It should be clearly understood that the forms of the invention hereindescribed are illustrative only and are not intended to limit the scopeof the invention. The present invention includes all modificationsfalling within the scope of the following claims.

We claim:
 1. A process for polymerizing an olefin and/or polymerizationan olefin and at least one or more other olefin(s) comprisingcontacting, under polymerization conditions, the olefin and/or theolefin and at least one or more other olefin(s) with at least onemetallocene catalyst comprising at least one transition metal componenthaving at least one moiety selected from the group consisting ofsubstituted or unsubstituted cyclopentadienyl, substituted orunsubstituted pentadienyl, substituted or unsubstituted pyrrole,substituted or unsubstituted phosphole, substituted or unsubstitutedarsole, substituted or unsubstituted boratabenzene, and substituted orunsubstituted carborane, and at least one co-catalyst component, anddinitrogen monoxide, wherein the dinitrogen monoxide is present in anamount sufficient to reduce electrostatic charge in the polymerizationmedium to a level lower than would be obtained in the absence ofdinitrogen monoxide.
 2. The process according to claim 1 wherein themetal of the transition metal component comprises at least one metalselected from the group consisting of Groups 3, 4, 5, 6, 7, 8, 9 and 10of the Periodic Table of the Elements, as defined herein.
 3. The processaccording to claim 2 wherein the metal is selected from the groupconsisting of titanium, zirconium, hafnium, vanadium and chromium. 4.The process according to claim 3 wherein the metal is selected from thegroup consisting of titanium, zirconium and mixtures thereof.
 5. Theprocess according to claim 1 wherein the metallocene catalyst issupported on a carrier.
 6. The process according to claim 5 wherein thecarrier is selected from the group consisting of silica, alumina,magnesium chloride and mixtures thereof.
 7. The process according toclaim 1 further comprising adding a halogenated hydrocarbon to thepolymerization medium.
 8. The process according to claim 7 wherein thehalogenated hydrocarbon is selected from the group consisting ofdichloromethane, chloroform, carbon tetrachloride, chlorofluoromethane,chlorodifluromethane, dichlorodifluoromethane, fluorodichloromethane,chlorotrifluoromethane, fluorotrichloromethane and 1,2-dichloroethane.9. The process according to claim 8 wherein the halogenated hydrocarbonis chloroform.
 10. The process according to claim 1 wherein thedinitrogen monoxide is added in an amount ranging from about 1 ppm toabout 10,000 ppm by volume.
 11. The process according to claim 1 whereinthe polymerization medium is gas phase.
 12. The process according toclaim 1 wherein the polymerization medium is slurry phase.
 13. Theprocess according to claim 1 wherein the olefin is ethylene and the atleast one or more other olefin(s) is selected from the group consistingof olefins having 3 to 16 carbon atoms.
 14. The process according toclaim 13 wherein the at least one or more other olefin(s) is selectedfrom the group consisting of 1-octene, 1-hexene, 4-methylpent-1-ene,1-pentene, 1-butene and propylene.
 15. The process according to claim 13wherein the interpolymer resulting from the polymerization of ethyleneand at least one or more olefin(s) comprises ethylene in an amount of atleast about 50% by weight of the interpolymer.
 16. A process forreducing electrostatic charge in a polymerization medium, thepolymerization comprising an olefin optionally and at least one or moreother olefin(s), at least one metallocene catalyst comprising at leastone transition metal component having at least one moiety selected fromthe group consisting of substituted or unsubstituted cyclopentadienyl,substituted or unsubstituted pentadienyl, substituted or unsubstitutedpyrrole, substituted or unsubstituted phosphole, substituted orunsubstituted arsole, substituted or unsubstituted boratabenzene, andsubstituted or unsubstituted carborane, and at least one co-catalystcomponent the process, comprising introducing into the polymerizationmedium dinitrogen monoxide in an amount sufficient to reduceelectrostatic charge in the polymerization medium to a level lower thanwould be obtained in the absence of dinitrogen monoxide.
 17. The processaccording to claim 16 wherein the metal of the transition metalcomponent comprises at least one metal selected from the groupconsisting of Groups 3, 4, 5, 6, 7, 8, 9 and 10 of the Periodic Table ofthe Elements, as defined herein.
 18. The process according to claim 17wherein the metal is selected from the group consisting of titanium,zirconium, hafnium, vanadium and chromium.
 19. The process according toclaim 18 wherein the metal is selected from the group consisting oftitanium, zirconium and mixtures thereof.
 20. The process according toclaim 16 wherein the metallocene catalyst is supported on a carrier. 21.The process according to claim 20 wherein the carrier is selected fromthe group consisting of silica, alumina, magnesium chloride and mixturesthereof.
 22. The process according to claim 16 further comprising addinga halogenated hydrocarbon to the polymerization medium.
 23. The processaccording to claim 22 wherein the halogenated hydrocarbon is selectedfrom the group consisting of dichloromethane, chloroform, carbontetrachloride, chlorofluoromethane, chlorodifluromethane,dichlorodifluoromethane, fluorodichloromethane, chlorotrifluoromethane,fluorotrichloromethane and 1,2-dichloroethane.
 24. The process accordingto claim 23 wherein the halogenated hydrocarbon is chloroform.
 25. Theprocess according to claim 16 wherein the dinitrogen monoxide is addedin an amount ranging from about 1 ppm to about 10,000 ppm by volume. 26.The process according to claim 16 wherein the polymerization medium isgas phase.
 27. The process according to claim 16 wherein thepolymerization medium is slurry phase.
 28. The process according toclaim 16 wherein the olefin is ethylene and the at least one or moreother olefin(s) is selected from the group consisting of olefins having3 to 16 carbon atoms.
 29. The process according to claim 28 wherein theat least one or more other olefin(s) is selected from the groupconsisting of 1-octene, 1-hexene, 4-methylpent-1-ene, 1-pentene,1-butene and propylene.
 30. The process according to claim 28 whereinthe interpolymer resulting from the polymerization of ethylene and atleast one or more olefin(s) comprises ethylene in an amount of at leastabout 50% by weight of the interpolymer.